SOLR-4839: Add upgrade notes, move entry to 5.2.0. Added entry for SOLR-7449
SOLR-4839: Add upgrade notes, move entry to 5.2.0. Added entry for SOLR-7449

git-svn-id: 308d55f399f3bd9aa0560a10e81a003040006c48@1676113 13f79535-47bb-0310-9956-ffa450edef68

apache/solr,apache/solr,apache/solr,apache/solr,apache/solr